1. Field of the Invention
The present invention relates to a milking machine for milking a cow and more particularly to a milking machine capable of measuring a flow rate of milk exactly.
2. Description of the Relevant Art
When a milking machine is employed to milk a cow, it is desirable to finish the milking immediately in view of the protection of the cow and the milking efficiency if the flow rate of milk is smaller than a predetermined value.
Heretofore, the milking operation is finished when a predetermined waiting time elapsed after the detected flow rate of milk is lowered to a predetermined value or less. In this case, Japanese Patent Unexamined Publication No. 59-169428, for example, discloses a finish control apparatus for the milking operation which employs an indicator to display the finish time of the milking operation.
However, the conventional apparatus applies the uniform waiting time to every cow to finish the milking and accordingly there occurs the case where the waiting time is too long or too short depending on characteristics of the cows. The too long waiting time means a long time of milking a cow vainly and affects the cow adversely. Conversely, the too short waiting time leaves milk in the udder of the cow to reduce the milking production and also affects the cow adversely. Thus, it is not possible to control the finish of milking for each cow exactly.
The measurement of the flow rate of milk during the milking is made on the basis of an electrical resistance value between a pair of electrodes provided in a milking line when current flows between the pair of electrodes. The decision to end milking is judged by detecting a resistance value increasing suddenly when the flow rate of milk is reduced to a predetermined value or less near the end of milking and by comparing a resistance value actually measured at this time with a predetermined reference resistance value to detect the reduction of the flow rate of milk.
However, an unusual cow such as a diseased cow with the mastitis generally produces milk having a high electrical conductance and accordingly the actually measured resistance value of milk may be largely different from that of a healthy cow. In this case, the flow rate of milk can not be measured exactly since the reference resistance value is constant, and the finish time of milking deviates from the usual time to further affect the cow adversely.